The present invention relates generally to a litter box, and particularly to a litter box in which soiled litter passes through a grate leaving clean litter behind.
Cats and other primarily indoor animals are typically trained to use a litter box for elimination of both liquid waste (e.g. urine) and solid waste (e.g. excrement). Liquid waste and solid waste are jointly referred to as “wastes.” When an animal uses a litter box, previously “clean” litter is now “soiled” litter. It should be noted that, in general, not all the litter in the litter box is soiled when an animal uses the litter box. Only the litter that has touched and/or absorbed the wastes is soiled litter. Removal of the waste and the soiled litter leaves clean litter.
Whereas litter boxes used to be filled with sand or ashes, litters are now made from a wide variety of materials such as clay, corn, silica gel crystals, recycled paper, wheat hulls, walnut shells, grass, and bark. One of the most common litters is “clumping” litter. Clumping litter (typically bentonite) is highly absorbent and forms solid clumps when liquid waste touches it. Examples of clumping litter are described in U.S. Pat. No. 5,188,064 to House and U.S. Pat. No. 6,745,720 to Rasner et al. Examples of commercially available clumping litter include PURINA® TIDY CATS® 24/7 Performance Clumping Cat Litter, sWHEAT SCOOP® Multi-Cat All-Natural Clumping Cat Litter, and ARM & HAMMER® SUPER SCOOP™ Clumping Litter. Although clumping litter makes litter box scooping and cleaning easy, it is dusty, non-biodegradable, and heavy. Clumping litter is also expensive. As an example, a month's worth of clumping litter for a single cat may cost between $10 and $40. Non-clumping clays are generally cheaper, but tend to get dirty faster because it is easy to leave bits of moist litter behind during removal.
Wood pellet litter may be made from lumber scraps that are heat-treated to remove toxins, oils, and allergens. Examples of wood pellet litter are described in U.S. Pat. No. 3,941,090 to Fry and U.S. Pat. No. 5,927,049 to Simard. An example of commercially available wood pellet litter is Dry Den™ Animal Bedding with Zeolites. Wood pellet litter has a naturally appealing scent (which helps control odor). On the other hand, wood pellet litter turns to “sawdust” when it gets wet. This “powderization” of the pellets makes it at least extremely difficult to remove liquid waste, particularly with scooping (including automated scooping). Wood pellet litter, therefore, must regularly be replaced in its entirety (as opposed to just removing the waste and the soiled litter). Compared to clumping litter and most other types of litter, wood pellet litter is relatively cheap. For example, assuming that all the wood pellet litter must be removed and replaced on a daily basis, as an example, a month's worth of wood pellet litter for a single cat may cost between $4 and $12.
Both manual litter boxes and automated litter boxes (also referred to as self-cleaning or automatic litter boxes) may use a physical separation process (e.g. raking or sifting) to separate the wastes and soiled litter from the clean litter. These separating litter boxes usually take advantage of the fact that the litter particles are considerably smaller than the solid waste. Further, these litter boxes use clumping litter that can be handled in the same fashion as the solid waste. (Without clumping litter, it is difficult or impossible to separate physically liquid waste or litter exposed to liquid waste from clean litter.) Physical separation of the small clean litter from the solid waste and the soiled litter (e.g. the litter clumped from its association with the liquid waste) is generally achieved by having the small clean litter pass through perforations that are sized to be large enough to let the clean litter pass through easily and yet small enough to retain the solid waste and soiled litter.
In using a manual litter box, solid waste and soiled litter is manually raked or sifted to leave clean litter behind. One example of this type of litter box is shown U.S. Pat. No. 4,325,325 to Larter, which describes two matching interconnecting litter boxes and a removable, perforated, separator plate that is placed between the boxes. Upon inverting the boxes, the separator removes the solid waste from the first container by allowing only the “cleansed” litter to flow through the perforated plate and into the second container. Another example is U.S. Pat. No. 3,908,597 to Taylor. This patent describes a litter box having double boxes with perforated bottoms and a slide-out solid divider. Removing the slide-out divider allows the “cleansed” litter to flow from one container to the other, at which point the top container is removed and the solid waste disposed of. The top container is then replaced with a cap and the whole stack inverted to repeat the process. Other patents for manual pet litter boxes (although some incorporate movable parts activated by handles, cranks, or levers) include U.S. Pat. No. 4,602,593 to Gross, U.S. Pat. No. 4,616,598 to Burniski et al., and U.S. Pat. No. 5,168,834 to Buschur. With manual litter boxes, owners may forget to clean the waste from the litter so that, in a relatively short time, the litter box may become full, may begin to smell, or both.
Animal owners often use automated litter boxes. Automated litter boxes, like manual litter boxes, may use a physical separation process (e.g. raking or sifting) to separate the wastes and soiled litter from the clean litter. For example, automated litter boxes may include a rake or comb that is normally maintained in a storage position at one end of the litter box. This rake is moved through the litter material in the litter box, and at the discharge end of the litter box the rake can move up and out of the litter material, discharging any clumps of waste collected by the rake into a disposal receptacle. Upon completion of the waste removal, the rake moves back to the storage position. Examples of automated litter boxes include those described in U.S. Pat. No. 4,096,827 to Cotter, U.S. Pat. No. 4,886,014 to Sheriff, U.S. Pat. No. 5,662,066 to Reitz, U.S. Pat. No. 6,082,302 to Thaler et al., U.S. Pat. No. 6,701,868 to Shepherd, U.S. Pat. No. 7,647,889 to Horanoff, U.S. Pat. No. 8,757,094 to Baxter et al., and U.S. Pat. No. 9,526,226 to Plazarte et al. Problems with these automated rake machines include rakes getting stuck, clumps of waste and/or litter sticking to the rake and/or the floor, the rake becoming dislodged, the rake not moving the waste all the way out of the portion that holds the litter, or a combination thereof. Other automated litter boxes rotate and sift the waste from the litter so that the clean litter is retained in the portion that holds the litter and the waste is emptied into the portion that receives the waste.